This invention relates to an .alpha.-type titanyl phthalocyanine composition used advantageously as a sensitive material in an image forming device such as a copying machine or a laser beam printer, to a method for the production of the composition, and to an electrophotographic sensitive material using the composition.
As sensitive materials for such image forming devices as copying machines, electrophotographic sensitive materials using such photoconductive substances as phthalocyanines have found extensive utility.
In recent years, the laser beam printer using a semiconductor laser as a light source thereof and enjoying various advantages such as permitting reduction in size of apparatus and enabling images of high quality to be quickly produced by a non-impact process has been disseminating. Various studies are now under way in search of photoconductive substances fit for use as sensitive materials available for the laser beam printer.
The electrophotographic process using the laser beam printer quality sensitive material comprises a charging step for uniformly charging a sensitive material by corona discharge, an exposing step for exposing the charged sensitive material through the image of an original to a semiconductor laser thereby forming on the sensitive material a latent electrostatic image corresponding to the image of the original, etc. Quantity production of electrophotographic copies is attained by repeating the electrophotographic process mentioned above.
In the charging step, the sensitive material is required to manifest a satisfactory charging property and suffer only from small dark attenuation. In the exposing step, it is required to exhibit high sensitivity to wavelengths approximately in the range of 780 to 820 nm, the wavelengths inherent in the semiconductor laser and suffer sparingly from residual potential after the exposure to the semiconductor laser. The sensitive material is also required to suffer sparingly from deterioration of the properties mentioned above during the course of repeated use.
As photoconductive substances capable of fulfilling these requirements, phthalocyanine compounds which exhibit high sensitivity to wavelengths falling in the aforementioned range of wavelengths inherent in the semiconductor laser. Some of the phthalocyanine compounds are metal-free phthalocyanines which are devoid of a central metal and the remainder phthalocyanine compounds are metal phthalocyanines which are possessed of a central metal. They are otherwise classified by the crystal form under .alpha. type, .beta. type, .gamma. type, etc.
They differ not only in stability but also in absorption spectrum, depending on the existence or nonexistence of a central metal, the kind of the central metal, and the crystal form. These differences have a significant effect upon the charging property and the sensitivity.
To be more specific, some of the metal-free phthalocyanines excel in photoconductivity and exhibit high sensitivity to wavelengths in the aforementioned range (about 780 to 820 nm).
The metal-free phthalocyanines possess a metastable crystal form. It is, therefore, difficult to obtain a sensitive material possessing stable properties from a metal-free phthalocyanine.
Metal phthalocyanines such as copper phthalocyanine occur in various crystal forms such as .alpha. type, .beta. type, .gamma. type, and .epsilon. type. It has been known that the .epsilon.-type copper phthalocyanine among other crystal forms possesses an absorption zone on the long wavelength side and exhibits spectral sensitivity also on the long wavelength side (Denshishashin Gakkaishi [Journal of Electrophotographic Society], Vol. 22, No. 2, page 111, 1984).
The copper phthalocyanine, however, is still deficient in sensitivity.
Sensitive materials which contain in the sensitive layer thereof titanyl phthalocyanine possessing titanium as a coordination metal like a composite electrophotographic sensitive material which is provided with a sensitive layer having .alpha.-type titanyl phthalocyanine dispersed in a binder have been proposed. As examples of such sensitive materials, a composite electrophotographic sensitive material which possesses a sensitive layer having .alpha.-type titanyl phthalocyanine dispersed in a binding agent (Japanese Patent Application Disclosure SHO No. 61(1986)-239,248) and an electrophotographic sensitive material which has an electric charge transfer layer superposed on an electric charge generating layer having a specific titanyl phthalocyanine dispersed in a binding agent (Japanese Patent Application Disclosure SHO No. 62(1987)-67,094) may be mentioned.
The electrophotographic sensitive materials which use as a photoconductive substance titanyl phthalocyanine of the sort described above exhibit appreciably high sensitivity to wavelengths in the aforementioned range of wavelengths inherent in the semiconductor laser and, at the same time, excel in electrical properties including the charging property.
The electrophotographic sensitive materials described above, however, pose as a problem the deficiency in sensitivity as well as in such electrical properties as charging property, dark attenuation, and residual potential.